A conventional and known fuel property detection device is configured to measure a capacitance of a gap between electrodes exposed to a fuel passage and to detect the property of fuel according to the measurement result.
For example, a fuel property detection device of U.S. Pat. No. 7,030,629 includes a fuel pipe, which forms a first electrode and has a fuel passage extending therethrough, and a second electrode inserted in the fuel pipe. This configuration of U.S. Pat. No. 7,030,629 defines a gap between the first and second electrodes exposed to the fuel passage, and the gap receives fuel flowing though the fuel passage. This configuration of U.S. Pat. No. 7,030,629 enables to detect the property of fuel according to a capacitance of the gap between the first and second electrodes, since the capacitance changes correspondingly to the property of fuel flowing into the gap.
In order to enhance the accuracy of the property detection based on the capacitance of the gap between the electrodes, it is conceivable to reduce the distance between the electrodes as much as possible to enhance sensitivity relative to change in the capacitance. Nevertheless, in the fuel property detection device of U.S. Pat. No. 7,030,629, when the distance between the first and second electrodes is reduced, fuel, which has been measured of its property, easily retains in the gap between the electrodes. Consequently, the fuel is hardly replaced with undetected fuel with the property being changed. Thus, fuel stack occurs to cause erroneous detection of the fuel property before being changed. Even though, it is noted that the fuel property detection device of U.S. Pat. No. 7,030,629 does not have a fail-safe function to address such erroneous detection.